Sam and Dean team up with their allies to bring down Dick Roman and the Leviathans. But not everyone makes it out intact...

The King of Hell, Crowley (Mark Sheppard) finds himself stuck in a Devil's trap by Dick Roman (James Patrick Stuart), the leader of the Leviathans. Crowley realizes that Roman knows about Sam (Jared Padalecki) and Dean Winchester's (Jensen Ackles) plan to create a holy weapon that can kill even Roman if Crowley's blood is added to an angel's blood and an Alpha's blood. Roman is also smart enough to work out that Crowley had a contingency plan in place in case Roman was able to destroy him. So, Roman offers Crowley and his demonic forces Canada in exchange for leaving America to the Leviathans.

Crowley produces an insanely long contract filled with sub-clauses for Roman to look over and sign while Sam and Dean begin examining records of dead Nuns to find one righteous enough that her bones can be used as a holy instrument to kill the Leviathans. Elsewhere, the ghost of Bobby Singer (Jim Beaver) continues to possess the housekeeper, Louise (Larissa Gomes) while making his way towards Roman's corporate headquarters. Because Crowley is in the Demon's trap, he is not able to answer the summons of Sam and Dean before Meg (Rachel Miner) arrives with Castiel (Misha Collins), who seems just as mentally unbalanced as he was previously.

Although Castiel is barely able to focus, he tells the Winchesters that the Leviathans now hold the prophet, Kevin Tran (Osric Chau) and that the host of angels protecting Kevin have all been killed. Just then, Meg notices that the Winchesters have summoned Crowley and she starts to panic right before Crowley appears and blocks her retreat. Crowley is also surprised and enraged to find Castiel there, but he quickly notes that the angel has apparently gone insane. Crowley even admits that he was held up because Roman had him in a Devil's trap and wanted him to give the brothers the blood of a minor demon instead of his own.

Crowley assures the Winchesters that the blood he is providing is his and he promises to destroy Meg in the future before departing. Elsewhere, Louise is briefly freed from Bobby's possession before he quickly retakes control of her body. Back at his corporate office, Roman seems to be well aware that Crowley will try to screw him, so he has his assistant, Susan (Olivia Cheng) bring him the arm of the real Dick Roman. Meanwhile, a young woman named Polly (Niki Wipf) is locked up with Kevin by his Leviathan captors, but she is too docile from the Leviathans' food additives to even engage in a proper conversation with Kevin.

After their captors take Polly and parade her in front of the visiting Leviathan leaders, Kevin picks the lock of his room and overhears the leaders' plan to get rid of healthy people like Polly by adding a new additive to the food supply. Polly dies horribly when the additive is injected into her system and Kevin is quickly recaptured by Susan. Outside, Sam and Dean use a backdoor security feed (provided by their brief hacker ally, Charlie). Unfortunately, they see that Roman has created several doubles of himself by having other Leviathans touch the arm of the real Dick Roman. Sam also spots Louise attempting to sneak into the building and he recognizes her as a maid from the hotel where Bobby abandoned them.

Sam confronts Bobby (in Louise's body) and tries to keep him from throwing her life away. Bobby nearly chokes Sam to death before realizing what he was doing and fleeing Louise's body. Later at the cabin, the Winchesters fill in Castiel and Meg on the latest developments, but Castiel once again refuses to fight. During his brief absence, Meg explains that Castiel is the only one who can tell the Leviathans apart by sight no matter whose body they're wearing. Shortly thereafter, Bobby's ghost reappears and apologizes for nearly killing Sam. He tells them to destroy the flask and banish his spirit from this world. The Winchesters comply with Bobby's last wish and solemnly watch him burn away.

Dean finds Castiel playing board games with himself and he finally manages to convince the fallen angel to help them finish Roman off once and for all. And because Roman is expecting them, they decide to announce themselves "loudly." To that end, the Impala is taken out of storage before it blasts through the front gate of Roman's corporate headquarters. Meg gets out of the car and begins killing Leviathans as Sam, Dean and Castiel sneak into the main building. Inside, Sam finds Kevin, who warns him that they have to blow up the Leviathans' lab to prevent their newest additive from being used on healthy people.

Outside, Meg stands triumphant over the Leviathans, but she is soon blindsided by two of Crowley's demons. Inside the building, Dean and Castiel find the real Leviathan leader posing as Roman and attempt to kill him with the holy weapon… which fails spectacularly. But just when Roman is feeling invulnerable, Dean produces the real weapon and stabs Roman through the neck while Castiel holds him. A strange energy buildup emanates from the fatal wound before Roman explodes. As the smoke fades, Sam and Kevin see that there is no sign of Dean or Castiel. Crowley then appears and he explains that the holy weapon "had a kick."

Crowley also has his demons take Kevin into their custody and teleport away, leaving Sam on his own to face the remaining Leviathans. Elsewhere, Dean wakes up and Castiel tells them that they are now trapped in Purgatory with all of the monsters, who are now closing in on them. Dean says that they should leave, but when he turns, Castiel is already gone.

Breakdown:

After dragging along for the entire seventh season of "Supernatural," the Leviathan storyline is finally over. I hope…

The ending of "Survival of the Fittest" suggested that there may be several Leviathan leaders still active who might try to replace Dick Roman and continue his plans for the human race. Or at the very least, they could give Sam a lot of problems as he tries to fight his way out of their stronghold by himself.

I've been fairly supportive of Bobby Singer's storyline this year, from his poignant deathbed episode to his return as an increasingly vengeful ghost. But if this was the end of Bobby's time on the show than he went out with a huge whimper. What was the point of bringing Bobby back as a ghost if the entire angle was just going to be squandered in his final appearance? If felt like there was a lot of territory worth exploring before Bobby finally decided to have the Winchesters banish his ghost.

About the only thing that this episode got right about Bobby was his goodbye scene with the Winchesters. Jim Beaver gave a standout performance while Bobby offered his last bit of advice and best wishes to the Winchesters before the camera stayed on Jared Padalecki and Jensen Ackles as they silently reacted to the destruction of Bobby's spirit. Moments like that are what make "Supernatural" worth coming back to.

Crazy Castiel was also a lot of fun, especially when he identified the Nun's bone by smelling it and when he presented ham sandwiches to Sam and Dean while mentioning how he comforted the pig before slaughtering it himself. There was also a strong scene between Castiel and Dean that helped heal the divide between them. Of course, Castiel bailing out on Dean in Purgatory was a step backwards for that relationship. But I highly doubt that Castiel would let Dean die that way.

On its own, there's nothing wrong with the idea of a cliffhanger ending where Dean and Castiel are stuck in Purgatory. The problem is that this show has already done cliffhanger endings with Dean and Sam trapped in Hell (or mysteriously returned from Hell, in Sam's case). It just seems like a rehash. And what were the Leviathans, really, if not slightly different demons with big teeth and a comical aversion to household cleaners? Any series that goes as long as "Supernatural" runs the risk of repeating itself at some point. But it's almost as if the writers don't even care about finding new angles anymore.

It was refreshing that Meg didn't betray the Winchesters and that she was right about Crowley being the next major threat on the show. It was also good to see the Impala again, even if it was sacrilege to let Meg drive it! All kidding aside, I'd like to see Rachel Miner stay on the show next season. There's something inherently amusing about Meg being one of the few real allies that Sam and Dean have left. I figured that Kevin would be on their team as well, but the writers need to find something else for him to do besides constantly being held hostage.

"Survival of the Fittest" was good enough for a season finale. But I'd love to see "Supernatural" recapture its earlier greatness in the eighth season next fall.